An ABS resin is an acrylonitrile-butadiene-styrene terpolymer which is widely utilized in a variety of fields including electric and electronic products, construction materials and automobiles due to excellent impact resistance, strength, chemical resistance and processability. However, an ABS resin is disadvantageously unsuitable for use in exterior materials because a butadiene polymer is used as a rubber, and thus has poor weather resistance.
Meanwhile, in order to obtain thermoplastic resins with superior physical properties, weather resistance and aging resistance, an ethylene unsaturated polymer should not be present in an acrylonitrile-acrylate-styrene graft copolymer. An ASA (acrylonitrile-styrene-acrylate terpolymer) resin employing a cross-linked alkyl acrylate rubber polymer was demonstrated to be suitable as a representative example of thermoplastic resins with excellent weather resistance and aging resistance. Such an ASA resin has superior weather resistance and aging resistance and is utilized in a variety of applications including automobiles, ships, leisure products, construction materials and gardening materials.
A method for preparing an ASA polymer with superior weather resistance and aging resistance is disclosed in German Patent No. 1,260,135. A core used for this method is a large-diameter latex of cross-linked acrylate with a mean particle diameter of 150 to 800 nm and a narrow particle size distribution. As compared to a polymer prepared using a small-diameter polyacrylate latex, a polymer comprising a large-diameter polyacrylate latex has improved notch impact strength, high hardness and reduced shrinkage. However, the large-diameter acrylonitrile-acrylate-styrene graft copolymer has a disadvantage of difficulty of coloring as compared to small-diameter acrylonitrile-acrylate-styrene graft copolymers.
Use of corresponding ASA polymers for preparing color articles is limited. That is, a pale pastel color is obtained rather than a vibrant color.
For reference, materials known to date have superior weather resistance and mechanical properties and improved colorability. However, improvement in colorability by these materials is yet insufficient due to use in conjunction with large-diameter acrylonitrile-acrylate-styrene graft copolymers that deteriorate colorability. Because these materials employ a cross-linked alkyl acrylate polymer as a rubber component, they cannot obtain a clear color due to excessively low refractive index of alkyl acrylate, as compared to styrene and acrylonitrile.
Use of a multi-layer alkyl acrylate rubber polymer including a diene rubber polymer in order to overcome this disadvantage is suggested in Japanese Patent Publication Sho. 47-47863, Japanese Patent Publication Sho. 59-49245, Japanese Patent Publication Hei. 3-66329 and the like.
However, these patents are disadvantageously unsuitable for preparation of resins with superior weather resistance because an alkyl acrylate polymer outer layer does not sufficiently surround a diene polymer inner layer.